In one type of filtering apparatus a filter is moved sideways through an access opening into a housing and into alignment with an outlet opening. Then the filter is pressed against the housing around the opening by means of pressure bars that are moved toward and away from the filter by mechanisms that include rotatable shafts extending out through the end of the housing beside the access opening. After a filter has been placed in the housing, a door for the access opening is clamped in place to seal the opening. Before or after this happens, the filter is supposed to be clamped in place by means of the pressure bars. However, it sometimes happens that the operator closes the door without making sure that the filter has been forced into sealing position around the outlet opening in the housing, resulting in leakage around the filter.
It is among the objects of this invention to provide a safety device for the type of filtering apparatus just described, whereby the door of the filter housing cannot be moved into final tightly closed position until the filter has been properly sealed in place.